1. Technical Field
The present invention relates to a sprinkler head which is activated in an event of fire to disperse water around for extinguishing a fire.
2. Description of the Related Art
A sprinkler head is configured such that a heat-sensitive decomposition structure of the sprinkler head is decomposed due to an unusually high temperature from a fire to release a valve element which is previously held in position by the heat-sensitive decomposition structure to allow water to be dispersed around for extinguishing a fire. A heat-sensitive material usable for the heat-sensitive decomposition structure of the sprinkler head may include a liquid and a low-melting point alloy.
When the liquid is used for the heat-sensitive decomposition structure in the sprinkler head, an alcohol may be employed as the heat-sensitive material. The heat-sensitive decomposition structure using the alcohol is referred to as a glass bulb type, in which an amount of alcohol, together with a small volume of air, is loaded in an ampule made of glass. In the structure of the glass bulb type, the ampule as described above is placed between a valve element and a main body of a sprinkler head to thereby support the valve element. In the structure of the glass bulb type, when a fire breaks out, the alcohol contained in the ampule is excited to come to a boil and thus evaporate, which in turn increases an internal pressure of the ampule and ultimately destroys the ampule. Consequently, this can release the valve element that has been held by the ampule. Although the structure of the glass bulb type is inexpensive and efficient, since this structure employs a mechanism in which the alcohol contained in the ampule is evaporated and the resultantly increased pressure destroys the ampule, only a small variation in the thickness and strength of the ampule, the amount of contained alcohol, the amount of contained air or the like may lead to a variation in time period until the destruction of the ampule; therefore a lack of stability is a concern in that the glass bulb type could not be always successfully activated at a predetermined temperature.
In the sprinkler head according to the prior art that has employed the low-melting point alloy for the heat-sensitive decomposition structure, the low-melting point alloy, when used as the heat-sensitive decomposition structure, can exhibit a superior property that it would introduce little variation in the activation timing, owing to the fact that the low-melting point alloy has a specific melting point depending on a specific composition or a compounding ratio of components of the alloy. The heat-sensitive decomposition structure using the low-melting point alloy includes a wrap joint type and a compression type.
The wrap joint type of heat-sensitive decomposition structure may refer to one that comprises two sheets of metals in an oval configuration that have been bonded together with the low-melting alloy. In the wrap joint type of heat-sensitive decomposition structure, the respective metal sheets at their ends are engaged with levers, with one of the levers holding the valve element, while the other of the levers is placed in abutment with the main body of the sprinkler head for supporting a pressing force against the valve element. In the sprinkler head incorporated with the heat-sensitive decomposition structure of the wrap joint type, when a fire breaks out, the low-melting point alloy is melted by the heat from the fire, and the metal sheets are separated to disengage the levers, so that the valve element is released to be open. Advantageously, the heat-sensitive decomposition structure of the wrap joint type, in which the heat-sensitive material employs the low-melting point alloy, can be activated more precisely with regard to the yield temperature, while on the other hand, it problematically lacks long-term reliability. That is, the heat-sensitive decomposition structure is always under a force to keep the valve element closed, as well as to provide a spring force to push the heat-sensitive decomposition structure sufficiently away so as not to interfere with a sprinkling operation when it is activated. However, the heat-sensitive decomposition structure of the wrap joint type, owing to its configuration that the two metal sheets are bonded together with the low-melting point alloy, could lead to peeling-off in the site of bonding due to the creeping phenomenon over a long time period.
The compression type of heat-sensitive decomposition structure may be such that the low-melting point alloy is loaded into a cylinder and further is pressed by a plunger, in which the cylinder and the plunger are configured to hold the valve element via other components or to engage the valve element to the main body. In the sprinkler head incorporated with the heat-sensitive decomposition structure of the compression type, when a fire breaks out, the low-melting point alloy is melted to allow the plunger sink into the cylinder, which in turn breaks the balancing between the components of the heat-sensitive decomposition structure to disengage them from one another, so that the valve element can be released to open. Advantageously, the heat-sensitive decomposition structure of the compression type, in which the heat-sensitive material employs the low-melting point alloy similarly to the wrap joint type, can be activated precisely with regard to the yield temperature, and additionally, owing to its configuration that the low-melting point alloy is filled in the cylinder and pressed by the plunger, the heat-sensitive decomposition structure of the compression type would not exhibit such a creeping phenomenon that could deform the low-melting point alloy, even if the low-melting point alloy is placed under strong compression force over a long time period. In view of those advantages as pointed out above, recently, the use of the heat-sensitive decomposition structure of the compression type has become mainstream.
The sprinkler heads employ a low-melting point alloy which is suitable for the specific location where the sprinkler head is placed. For example, the sprinkler head to be placed in an ordinary building, such as a high-rise apartment building or a department store, may employ such a low-melting point alloy having a relatively lower melting point in a range of 70-75° C. in order to be activated as quickly as possible to provide an initial stage extinction. In this regard, even in the ordinary building, specifically at a location above a stove burner in a kitchen or adjacent to a hot air outlet of a heating apparatus, the use of the low-melting point alloy having the melting point as low as 70-75° C. may lead to problematic situations. For example, when the temperature of the environment around the sprinkler head rises proximally to the melting point, the sprinkler head would be undesirably activated to disperse the water around, in spite of no fire being recognized, or when the temperature rises not as high as the melting point or higher but at least nearly to the melting point of the low-melting point alloy, the mechanical strength of the low-melting point alloy would be extremely decreased. Accordingly, it may cause the separation of the two metal sheets in the wrap joint type, or the softened low-melting point alloy to be crushed in the compression type. To avoid the problems as mentioned above, the low-melting point alloy having the melting point in a range of 90-100° C. is used at a location subject to a rising temperature, such as those in a kitchen or adjacent to a hot air outlet of a heating apparatus.
In the sprinkler head according to the prior art, most of the low-melting point alloys used in the heat-sensitive decomposition structure are those containing Pb or Cd. For example, the low-melting point alloy having the melting point in a range of 70-75° C. may be represented by 50Bi-12.5Cd-25Pb-12.5Sn (melting point at 72° C.) and the low-melting point alloy having the melting point in a range of 90-100° C. may be represented by 52Bi-32Pb-16Sn (melting point at 96° C.)
If should be noted that, the sprinkler head, in general, is kept installed as it is in the building as long as no fire occurs, but is replaced with a new one when it brings about unpleasant exterior appearance or it no more satisfies the authorized design rules, and those old ones may be scrapped. However, disposed sprinkler heads could cause pollution of underground water due to the Pb or Cd used in the heat-sensitive material for the heat-sensitive decomposition structure of the sprinkler head. If human beings drink the underground water containing the Pb or Cd over many years, undesirably the Pb or Cd are accumulated in a human body and possibly lead to lead or cadmium poisoning. In consideration of the above fact, there has been a demand for the sprinkler head comprising the heat-sensitive material completely free from the Pb or Cd in the construction industry as well as in the fire control equipment industry.
The applicant of the present invention had proposed an innovative sprinkler head characterized in using no Pb or Cd in the heat-sensitive material for the heat-sensitive decomposition structure, but employing a low-melting point alloy for the heat-sensitive decomposition structure, which comprises two or more metals selected from a group consisting of Sn, Bi, In, Zn, Ga and Ag (Japanese Patent Laid-open publication No. 2002-078815).